1. Field of the Invention
The present invention relates to a cathode ray tube apparatus and, more specifically, to an apparatus for cooling a cathode ray tube, particularly a high-luminance cathode ray tube used for color projectors. Still more particularly, this invention relates to an improved space-defining structure for enhancing the cooling effect on the front panel of a cathode ray tube which includes an expansion chamber outside of the field of vision of the cathode ray tube for permitting expansion of the cooling medium confined within the space and chamber during prolonged operation.
2. Description of the Prior Art
A cathode ray tube used for color projectors is constructed so that a high luminance optical image reproduced from a video tape recorder, for example, can be obtained by increasing the energy of an electron beam colliding with a surface of a fluorescent screen. Such a fluorescent screen is made from a panel, such as a glass panel, on which is applied a fluorescent substance. However, since the front panel or the glass panel of the cathode ray tube on which the fluorescent substance is applied is formed relatively thick so as to absorb x-rays, a significant amount of heat is readily generated from the front panel. When the cathode ray tube is in operation, the generated heat is not effectively emitted, resulting in a temperature rise in the front panel, and in particular in the center of the front panel.
As a result of such a significant temperature rise, a phenomenon known as thermal extinguishment occurs. According to such phenomenon, the luminescence of a fluorescent substance decreases with increasing temperature on the front panel. Thus, it is well known that the presence of this phenomenon will deteriorate the white balance of the cathode ray tube and deteriorate the picture quality of an optical image, and in particular that of a projected optical image.
In addition, when the temperature on the front panel of a cathode ray tube rises, the fluorescent substance applied to the front panel may peel away or be disengaged from the front panel. Accordingly, a temperature rise of the front panel creates an additional problem for attention.
To address these problems, an improved cathode ray tube apparatus has been proposed in Japanese Published Utility Model Application No. 59-7731. In that published application, a device is shown in which a space formed between the front panel of a cathode ray tube and a transparent panel located forward of the front panel is filled with a cooling medium to conduct heat to a metal frame associated with the cathode ray tube to serve as a heat sink. In the cathode ray tube apparatus as described, however, a sufficient quantity of the cooling medium is used to enhance the cooling effect of the front panel and generally fills the confined cooling medium space. The cooling medium, on the other hand, readily expands in volume with increasing temperature on the front panel. Thus, another problem exists in accommodating the expansion of the cooling medium in that the cathode ray tube apparatus may explode or the frame may become deformed due to high temperature. In the situation in which the front panel, the transparent panel, or the metallic frame are deformed, another problem results in that when the transparent panel is replaced with a lens, the distance between the front surface and the lens changes resulting in the projection of an unfocused optical image on a screen.
The arrangement of the prior art cathode ray tube apparatus will be described in further detail hereinafter with reference to the attached drawings and in the detailed description.
It is thus an overall object of the present invention to provide a cathode ray tube apparatus in which heat generated on the front panel can effectively be conducted to the metallic frame without deforming the front panel and the metallic frame and thus avoid deteriorating the quality of optical images.
It is an additional object of this invention to provide a cooling apparatus for a cathode ray tube which defines an air or expansion chamber associated with a defined space relative to the surface of the cathode ray tube to permit expansion of the cooling medium from the space to the chamber.
It is still another object of the invention to provide a structure for a cathode ray tube in which an expansion chamber is provided to accommodate expansion of a heated cooling medium in a direction which leaves unaffected the distance between the tube and its lens.
These and other objects of the invention will become apparent from the detailed description of the invention which follows, taken in conjunction with the accompanying drawings.